The present invention relates to a novel method and apparatus for performing accurate vehicle wheel alignment procedures. More specifically, the present invention relates to a method and apparatus for detecting, displaying, and/or compensating for transient undesired changes in suspension angle measurements caused by compression forces incident to an alignment operation.
When a vehicular wheel alignment is performed, several alignment related operations may induce transient suspension alignment angle changes. These changes are viewed as undesired deviations from true measurements. This is because in an ideal wheel alignment procedure, the only factor causing changes in alignment angles ought to be the mechanic's own deliberate adjustment of those angles.
The most prominent operation that induces these deviations and transients is lifting the vehicle leaving the wheels unsupported. Some examples of operations involving lifting the vehicle are wheel runout compensation and general alignment angle adjustment procedures (such as for camber, caster, SAI, or toe) for vehicles for which it is desirable to have the weight of the vehicle off its wheels. U.S. Pat. No. 4,180,915, issued to Lill et al., describes a prior art runout compensation operation. When the vehicle is lowered, the vehicle's suspension does not necessarily return to its original condition. The sensed alignment angles change after the vehicle is raised and then lowered even though no adjustments have been made. Worse, if adjustments have been made, the values obtained while the vehicle is lowered do not reflect the adjustments made while the vehicle was lifted. This is due to certain compression and decompression forces incident to the lifting and lowering. In sum, the suspension must be returned to its original condition at which the vehicle is driven. If further alignment angle adjustments are performed before the suspension is returned to its original condition, they will not be correct. Because of this phenomenon, some vehicle manufacturers recommend that their vehicle not be lifted off its wheels during a wheel alignment. For such vehicles, this removes a potentially valuable and time saving aid for the wheel alignment mechanic.
Other operations induce such deviations as well. For example, caster and SAI (steering axis inclination) swings often require that the steerable wheels be turned ten degrees to the left and right. The toe out on turns operation and the measurement of the Ackerman principle similarly usually require turning the steerable wheels. The maximum turns operation usually requires that each wheel is turned to its maximum turn angle. Indeed any operation that requires displacement of the wheels in translational space or about the steering axis might cause such transient suspension alignment angle changes. Such operations can cause the suspension to undergo certain compression and decompression forces that cause the sensed alignment angles to change.
Jouncing (bouncing) the suspension is the traditional way of overcoming these deviations and of restoring the vehicle wheel alignment to its normal condition. Jouncing induces a sharp impulse into the system that has the effect of undoing the error-inducing compressions. Until now, mechanics had no guidance on when and how much to jounce the vehicle. Sometimes mechanics wrongly omit the jouncing step. This omission virtually assures that the above mentioned errors will infect the alignment procedure. Sometimes mechanics jounce only once where more than one jounce is necessary to smooth out the transient alignment angle deviations. What is needed then is a way to monitor, warn of, and/or compensate for deviation angles caused by these transient forces. What is also needed is an apparatus that can instruct an alignment mechanic on when and how much to jounce a vehicle.
It is an object of the invention to overcome the above disadvantages and to provide a method and apparatus to monitor deviation angles caused by undesired compression forces during a wheel alignment operation.
It is another object of the invention to warn a mechanic when such deviation angles exceed a threshold acceptable value.
It is still another object of the invention to instruct the mechanic to jounce the vehicle until the undesired compression forces that cause the deviation angle are eliminated.
It is yet another object of the invention to provide more accurate alignment procedures that are not infected by transient suspension alignment angle changes.
It is a further object of the invention to prompt and lead a mechanic through a procedure that accomplishes the foregoing objects.
It is a still further object of the invention to provide an apparatus that accomplishes the foregoing objects.